1. Field of the Invention
The present invention relates to a gasket in use for hard disk drive (referred to as "HDD" hereinafter) unit and, in particular, to those in use for HDD unit which are integrally assembled with a cover case of an HDD unit.
2. Brief Description of the Prior Art
FIG. 7 (PRIOR ART) is a cross-sectional view showing a partial structure of an ordinary conventional gasket of this type. In FIG. 7, a numerical sign 11 stands for a metallic base cover, 14 stands for a plastic resin layer having a vibration suppressing function, 15 stands for a metallic substrate which is laminated through the plastic resin layer 14 onto an external surface (a rear surface in FIG. 7) of the metallic base cover 11. A through-hole 12 is opened on a desirable portion of the base cover 11 and penetrates from an internal surface (a front surface in FIG. 7) of the metallic base cover 11 to an outermost surface (a lowermost surface in FIG. 7) of the laminated metallic substrate 15. A rubber 13 is embedded in the through-hole 12, which penetrates through the metallic cover case 11, plastic resin layer 14 and the metallic substrate 15, to further protrude internally (upwardly in FIG. 7) toward a main body case of the HDD unit and to further protrude externally (downwardly in FIG. 7) to an open air ambient. A numerical and alphabetic character 13a represents aforesaid externally extruded portion of the rubber 13.
FIG. 8A (PRIOR ART) is a plan view and FIG. 8B (PRIOR ART) are a cross-sectional side view showing respectively a whole constitution of the conventional gasket mentioned above. The rubber 13 embedded in the metallic base cover 11 is provided with the desired shape and is stacked with the main body case of the HDD unit unshown in the figures on an opposite side of the externally protruded portion 13a thereby to seal an interior of the HDD unit.
However, since the protruded rubber portion 13a extrudes outwardly from the base cover 11 in the conventional gasket mentioned above, the rubber 13 is highly liable to be partially broken due to a contact with or an impact from obstacles which are located outside. When a breakdown of the rubber 13 begins at the outwardly extruded portion 13a then propagating into an inside of the rubber 13, a serious problem that a spatial continuity takes place from an internal sealed portion of the HDD unit through the broken portion of the rubber 13 and the through-hole 12 to the open air ambient which extends to be a leakage arises.
Since the through-hole 12 is provided entirely over the base cover 11, another problem that it is very difficult to open the through-hole (anchor-hole) if the metallic plates 11 and 15 are thick arises. On the other hand, when an adhesive is employed instead of the through-hole, a still another problem arises that gases included in the adhesive evaporate into the interior of the HDD unit.